The following paragraphs contain some discussion, which is illuminated by the innovations disclosed in this application, and any discussion of actual or proposed or possible approaches in this Background section does not imply that those approaches are prior art.
Natural resources such as oil and gas residing in a subterranean formation or zone are usually recovered by forming a wellbore that extends into the formation. The wellbore is drilled while circulating a drilling fluid therein. The drilling fluid is usually circulated downwardly through the interior of a drill pipe and upwardly through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore.
Cementing is a common technique used in wellbore operations to isolate or secure particular areas of a wellbore from other areas of a wellbore (zonal isolation). This type of cementing is typically performed by pumping a cement slurry into the annulus between the outside surface of a pipe string and the inside formation surface or wall of a wellbore and allowing the cement to set into a hard mass (i.e., sheath). Cement slurries typically contain cement, water, and various additives that can be tailored based on the type of cementing operation desired. The cement sheath attaches the string of pipe to the walls of the wellbore and seals the annulus, allowing a wellbore to be selectively completed.
However, cement can sometimes experience shrinkage that creates gaps between the cement and casing, resulting in loss of zonal isolation. Expansion additives are often added to the cement slurry in order to promote bonding integrity between the cement and the casing. Good bonding between the cement and the casing helps in achieving zonal isolation, controlling gas migration, protecting the casing from corrosive conditions and sustaining wellbore integrity. Poor bonding can limit production from the well and reduce the effectiveness of any stimulation treatments.
A large variety of materials have been used or proposed as cement expansion additives. For instance, common cement expansion additives include calcium sulfate hemihydrate, sodium sulfate and magnesium oxide. Generally, such materials provide cement expansion, however, such expansion is gained at the expense of either impaired compressive strength development or increased slurry viscosity. Furthermore, the growth of the petroleum industry has created a need for the recycling of many of the byproducts of petroleum processes. Therefore, it would be advantageous to use a petroleum process by-product as an expansion additive that provides adequate expansion, while simultaneously not affecting other desirable cement properties.